Electrical communicating system



HUGO [\Lf LIN-HUL- :55: V c. R. GAUTHIER ELECTRICAL COMMUNICATING SYS'IBI Original Filed Nov. 22, .1919

4 Sheets-Sheet 1 INVENTQR (7065 7?, Gen/finer 'z m svs UnUuU lU-l l-lU-IIVI- May 13, 1930.

c. R. GAUTHIER ELECTRICAL- COMMUNICATING SYSTBI Original Filed Nov. 22, 1919 4 Sh oots-Shoot 2 EN 6 C7066 7?. gal/Lifer ATTORNEYS May 1 1930- c. R. GAUTHIER ELECTRICAL COIIUNICATING SYSTEI 4 Sheds-Sheet 3 Original Filed Nov. 22. 1919 INVENTOR May 13, 1930. c, u'n- 4 V 1,758,570

ELECTRICAL COINUNICATING SYSTEM Original Filed Nov. 22. 1919 4 Sheets-Sheet 4 INVENTOR Crosby 7?. fiau 7610' ATTORNEYS Patented PATENT 'orrlcs CROSBY B. GAUTHIEB, O1 RIDGEWOOD, NEW JERSEY, ASSIGNOIB, BY MESNE ASSIGN- MENTS, TO FEDERAL TELEGRAPH COMPANY, A CORPORATION OF CALIFORNIA.

ELECTRICAL OOIEHUNICATDIG SYSTEM Originalapplication iiled Iovember 22,:1819, Serialll'o. 840,020. I Patent No. 1,558,919, dated September 8,

' 1925. Divided and this application filed September 5, 1925. Serial For 54,741.

This invention relates, in general, to electrical signaling systems, such as telephone and telegraph systems, and is directed more particularly to such a s stem wherein radio and metallic-line transmission, conjointly, are em loyed.

is application is a division of my copending application for U. S. Letters Patent Serial No. 340,020, filed November 22, 1919, on which United States Patent N 0. 1,552,919 was granted September 8,1925.

One object of this invention is the provision of an economical and reliable system whereby telephone or telegraph communication can beestablished and maintainedbetween moving vehicles and distant stationary points or between distantly separated moving vehicles, as for example, two railroad trains.

Another object of the invention is the pro vision of a telephone system which will permit telephone subscribers in distantly separated localities to transmit s eech or the like through the medium of ra io stations and the provision of means for enabling the controllin operators to talk and listen either on the ra io circuit or on the wire circuit.

One of the principal features of the invention relates to the provision of a telephone system wherein a plurality of radio stations and a plurality of telephone exchanges are situated at intervals along and operatively' associated with a'metallic transmission line and wherein means are provided for transmit-ting signals over the transmission line and into the ether from any of the tele hone exchanges through the medium of al the radio stations simultaneously.

Another of the principal features of the invention consists in the provision of a system for transmitting signals to and from moving vehicles, as for example, between distantly separated trains, or between a train and a distant station. According to this feature of the invention there is preferably provided one or more metallic transmission lines along the route of the vehicle, as for instance along a railroad track. A source of high frequency current on the vehicle or vehicles, means for suitably modulating the high frequency current in accordance with least semi-private communication and e im-' inating to a lar e extent the uncertainties in-- herent in long istance radio transmission.

Still another of the-principal. features of the invention relates to an arrangement whereby a radio station or stations can-be selectively'connectedto a metallic transmission line or lines under the control of a distant operator. This is accomplished, preferably, by providing at each radio station a suitable selecting device or devices which is or are operable over a circuit extending to a distant control station, as for instance, a telephoneexchange.

According to present practice in this art high frequency oscillations are produced controlled or modified in accordance with signals or impulses to be sent and transmitted to a distant station. It is often desirable to be able to control the source of oscillations from a remote point such as an operators switch board. A feature of this invention is a remote control ofthe source of high frequency oscillations.

There are still other features which will be readily understood from the detailed description hereinafter.

The many novel features embraced invthis invention are far-reaching in their scope and are applicable in many embodiments other than that which will be described, and I therefore do not wish to be limited except as indicated by the appended claims.

The embodiment of the invention which has been chosen for a detailed description is a telephone system particularly adapted for use on railroads and which may be connected with the usual telephone systems such as the Bell System, thereby providing telephone service for passengers and trainmen on moving trains. Incidentally the invention is also adapted for train dispatching service.

T e specific embodiment 0 this invention comprises a plurality of radio stations distributed alor. a railroad at relatively short intervals, each radio station being equipped with radio transmitting andreceivmg ap paratus; one or more trunk lines extending along the railroad, at least one end of which connects with an operating. or control station which may conveniently be a telephone exchange and means under the control of an operator at the control station whereby the radio apparatus at each of the radio stations can be connected to and disconnected from the trunk line as required. The trains on the railroad are equipped with radio transmit ting and receiving apparatus and the control station isequipped with essential telephone apparatus.

Telephone communication is established between parties on the trains and the operator at the control station through the medium of the operators telephone apparatus, the trunk line, the transmitting and receiving apparatus at the radio stations and the transmitting and receiving apparatus on the trains.

The transmitting range of each radio station is preferably quite s ort; It need be only a trifle more than half the distance between radio stations. In other words, if the radio stations are spaced five miles apart, the transmitting range of each radio station need be and is preferably onl a trifle over two and one-half miles in eac direction.

Communication is established through the medium of any one radio station, only while a trainiswithintherangeofthatstation. When a train passes out of the range of one radio station and into the range of a succeeding radio station, the first radio station is disconnected from the trunk line and the second radio station is connected thereto etc.

The advantage of using a plurality of radio stations equipped with short range transmitting apparatus will be obvious to those skilled in the art. Interference is largely eliminated by this system and communication can be established vover long distances. The possibility of messages being intercepted by stations ion which they are not intended is also reduced to a minimum by the use of short range apparatus. The transmitting apparatus carried by the trains is, of course, also of the short range variety.

Another feature of this system comprises the use, in connection with the aforementioned parts of the system, of a listening-in line extending along the railroad, at least one end of which connects with a control station. The receiving apparatus at each idle radio station is normally connected to the listening-in line and the controlling operators telephone set can be connected thereto. The object of the listening in line is to rovide means whereby parties on trains on t e railroad can call the cont-rolling operator, and whereby the controllin operator can .talk through the medium 0 several radio stations simultaneously whenever it becomes necessary to locate a train. Upon receiving a call from a train the controlling operator selects an. idle trunk line and connects thereto the radio station nearest the train. The provision of a listening-in line reduces the number of trunk lines necessary on a railroad where there are a large number of trains travelling at the same time. For example, if there were-a maximum of say twenty trains travellingat one time over a certain railroad in order to provide communicating means for every train, without using the listening-in line it would be necessary to .provide twenty trunk-lines. But the probabilities are that not more than five of, these trains would require a connection at any one time and therefore five trunk lines and a listening-in line would .be sufficient Another feature of this system is a wavelength changing device. The radio appara-,

tus is preferably arranged too erate on a number of difl'erent wave lengt In the drawin "accompanying this specification, the re '0 circuits are shown arran ed for operating on four different wave lengt course, any desired number of wave lengths can be provided for. The wave length changing device comprises an electro-magnetic step by step' mechanism co-operating with a number of movable switch members, the energizing circuit of thestep by step mechanism being operable by the operator at the control station. In the particular arrangement described herein, this mechanism is operable only when the radio station with which it is associated is connected to a trunk line. When a radio station is disconnected from a trunkline it is thereupon automatically connected to a listening-in line and the wave-length chan 'ng mechanism is automatically restore to its first or normal position. Thus. every idle radio station is set to operate on the same wave-length. This is desi ated the listening-in wave length. The ra io apparatus at each radio station is referably adjusted to operate on a correspon ing wavelength for each corresponding position of the wave length mechanisms.

As reviously stated, means are employed where y the various radio stations can be connected to and disconnected from a trunk-line as required.

, Assuming that communication has been established with a train, as it proceeds along the road, one radio station after another will be successively connected to and disconnected from a trunk line. The preferred means whereby these connections and disconnections are accomplished comprises the use of electro-magnetic selector mechanisms, the operationof which is under the control of an operator at the control station. The selector mechanisms or, briefly, selectors'operate on combinations of electrical impulses and in the circuit herein described the selectors are of the biased polarized type, that is they operate only on combinations of unidirectional electrical impulses and each selector will re spond efiectively only to pulses flowing in a definite direction throu h its coils. rents flowing in op osite irections through a circuit are sometlmesdesignated, for convenience, as positive and negative currents and this designation will be used hereinafter. Each selector, then,- will respond only to cur? rent impulses of a definite polarity, that 1s, ositive or negative, and will not be affected y impulses o opposite polarity. The selectors at eve tion operate on impu see of like polar ty.- For example, considerin four succeeding 5 radio stations A, B, C an D, the selectors at A and G will respond to impulses of like polarity, say positive impulses, and the selectors at stations B and D will res nd to impulses of like polarity, but of t e polant to opposite to that to which A and C respon that is B and D will respond to negative impulses.v If it is desired to connect radio station A to a trunk line, a definite combination of positive impulses are sent over the selector circuit and the selector at A'will operate and close its local circuit, thereby connecting the radio apparatus at A to the trunk-line and simultaneously disconnecting the radio apparatus from the listening-in line. As 4 soon as a communicatin train has passed out of the normal rangeo A, it is necessary to connect, B to the trunk line and disconnect A therefrom. The selector at B is operated by sending out a definite combination of negative impulses and as stated before the negative impulses will have no effect on the selector at A. Therefore, B is connected to the trunkline before A.is disconnected therefrom. Immediately after the requisite combination of negative impulses to operate the selector at B have been sent out, one additional positive impulse is sent out and this operates the selector at A to restore it to nor-- mal. Upon the restoration to normal of the selector at A, that station is disconnected from the trunk-line and connected to the listening-in line. By this arrangement it will be seen, a continuous connection is maintained, there being no interruption due to transferring from station to station.

Selectors operating on combinations of electrical impulses are well known in the art. For a description of such a selector reference is made to United States Patent 1,244,544 to Charles S. Rhoades,Jr.

alternate radio sta Impulse sending devices are also well known in the art and require no description.

tlons an they will be released automaticaL 1y when the train enters the range of the re spective' radio stations. Thereby the o erator is relieved of the necessityof watching signal lamps indicating the passage of the train from section to section.

An installation in accordance with this invention would ordinarily include a number of control stations. For example, an installation between Albany andBuflalo would be likely to include control stations at Albany, Utica, Syracuse, Rochester and Buffalo. As-

suming that a train is roceeding from Albany to Buffalo, from t 0 time it leaves Albany until it reaches Utica, conversations with that train can be handled by the operators either at Albany or Utica 'as required.

,If, for instance, a passenger on the train wishes to talk with a tale hone, subscriber in New York, the'call wi be handled by an Albany operator, but if the passen er wishes to talk. with a telephone subscri er in Bufi'alo, the call will be handled by'a I Utica operaton Considering the first case, that is a connection between the train and a New. York telephonefsubscriber, the call will'be handled by an Albany operator as long as the'train remains in the d1vision between Albany and Utica, but if the communication continues after the train passes Utica, then the control of the operation will be transferred from Albany to Utica and the latter 0 erator will continue to handle the call unti the train reaches the next control station, namely, Syracuse wh'en an operator at the latter station will take it up.

To establish communication between two trains in the same division, that is located between succeeding control stations, the operator appropriates two idle trunks in that division and connectsthe two to ther by means of a suitable cord circuit. he radio station nearest one of the trains is then connected .with one of the trunks, and the radio station nearest the other train is connected to the other trunk. Where the trains are in different divisions, the trunks are extended through the control station or stations, as the case may be, by means of the cord circuits. Where the trains are in adjacent divisions, the operations involved in connectingthe radio stations to the trunks and l trunk, and

chan ing connections as the trains proceed may e controlled by one operator, but where the trains are in distantly separated divisions, the operators at each of two control stations will be required to establish and maintain the connections.

Any suitable radio transmitting and receiving circuits can be used with this invention. the drawings accompanying this specification is based on that shown in United States Patent No. 1,273,789 to William C. White and the receiving circuit is one well known in the art. No detailed description, therefore, will be required for an understanding of these circuits. Substantiall the same radio circuits as are provided at t e radio stations would also be provided on the trains except for obvious modifications, as for instance, the remote control wave length changing arrangementwould not be provided on the train. It is therefore thou ht that there is no necessity for showing the radio circuits for use on the trains.

No provision is shown for amplifying the received signals, but it will be obvious that amplifiers can be used if required.

Provisions are shown in the circuits for operating the radio transmitting apparatus and the radio receiving apparatus, alternately. This provision comprises a transmitting and receiving relay, one at each radio station, the energizing circuits of which arecontrolled b -the operators at the control stations. T e transmitting and receiving apparatus is arranged to operate alternately in order to prevent the well known howling effect which might otherwise result. The transmitting and receiving relay will be hereinafter referred to as the T & R relay.

Referring to the.drawings-Fig. l is a fragmentary general arrangement showing two radio stations, with associated antennae and selector apparati, two trunk-lines, a listening-in line, a control station connecting with the lines, a railroad track with a passing train indicated thereon in dotted lines, and lamp signals at the control station for indicating the positions of trains. Many of the-details are omitted from this figure.

Fig. 2 is a circuit diagram of a complete radio station with connections to trunk lines, listening-in lines and lines serving the T & R relays, selectors and wave length changing mechanisms.

Fig. 3 is a fragmentary circuit diagram showing a trunk line connecting two control stations and impulse sending devices associated with one of the control stations together with a circuit arrangement illustrating the operation of one selector at a radio station. The operating circuit for a wave length mechanism and a T & R relay are here shown. Jacks forming terminals of the signal lamps for indicating the The transmitting circuit shown in 4, 5, 6 and 7 will be operative condition of the trunk line and a talking cord circuit .at one of the control stations are shown. A trunk leading from one of the control stations to a local telephone ofiice and part of a cord circuit at the local telephone office are also shown.

Fig. 4 illustrates the modification for the im nlse sender hereinbefore referred to.

Figs. 5, 6 and 7 show the Wave-length changing mechanism/of which Fig. 5 is a plan view of one of the radial switches.

Fig. 6 is a side elevation showing five radial switches, arranged in superposed relation to each other.

Fig. 7 is a sectional view on line 7--7 of Fig. 6, showing the electro-magneticstep by step mechanism whereby the rotatable ratchet member is driven.

Before embarking upon a the operation of the system, a brief description of the mechanisms illustrated in- Figs.

iven.

There is represented in Fig; 51-1111 ordinary impulse sending key of the ,type employed in train dispatching system? except that a simple provision is shownfor rendering the o eration of the key semi-automatic. The disc 146is integral with the windin handle 145, and .is provided: with a-lug 14 which bears a ainst a shoulder of armature 148 and is there y prevented from unwinding. The key is wound by turning in the direction indicated by the arrow, and in unwinding turns in the opposite direction. It will be quite clear from the drawin that when electromagnet 149 is energize armature 148 is attracted, and the key is thereupon free to unwind. 'The impulses are sent while the key is unwinding. Y

The wave length changing switch of Figs. 5, 6 and 7 comprises five contact wiper arms 13, 99, 100, 101 and 102, each of which is operatively and individually associated with a set of four fixed contact oints. All the contact wiper arms are insil latively mounted on a common rotatable shaft, to the end of which is secured a ratchet member 127. The mechanism for operating the ratchet member comprises a stepping pawl 125, which is pivotally attached to the armature 160 of the stepping magnet 109. 126 is a holding pawl, and 119,

120 are releasing magnets. Each energize.- tion of stepping magnet 109 will eifect a forward movement of stepping pawl 125, and will accordingly step ratchet member 127 forward. The lattter is held many of its forward positions by holding pawl 126, and may be released by energization of electromagnets 119 and 120, whereupon it is restored to normal, together with the contact wiper arms, by the restoring spring 128. It will be understood that the several contact wiper arms engage successive fixed contacts for each successive forward step of the ratchet member.

In the following description of operation description of of this invention, itwill be assumed that a its contact, conductor 165, winding of selector calling party on a train running from Albany to Bufialo wishes to communicate with atelephone a subscriber in Albany. The train is situated somewhere between Albany and Utica and proceeding toward the latter city. Referring to Fig. 1 of the drawings-4 is the train: 2 and 3 are sections of track insulated at point 4; 5 is the control station at Albany; 6 is the antenna associated with radio station A. Radio station B is similar in all respects to radio station A and will therefore require no separate description. 135 is the radio apparatus at radio station A. 17 is the-T'& R relay the contacts of which are shown in transmitting position. 35 and 131 are two trunk lines and 26 is a listening-in line, terminating in jack 27. 21 and 24 are relays controlling the connection of the radio apparatus with the listening-in line. 59 and 110 are relays controlling the connection of the radio apparatus with the trunk-line 35 and 131 respectively. 49 is a relay for cutting off selector 36, and 60 is a relay for cutting off selector 64. All the above. rela s except relay 17 are in local circuits control ed by selectors 36 and 64respectively.

The train 1 being in section 2 of the track and therefore within the range of radio station A, the call from the train is picked up by the antenna 6 and receiving apparatus R at radio station A. Referring to Fig. 2, the antenna circuit for the listening-in position consists of antenna 6, inductance 7, condenser 9, switch 13, inductance coil8 and ground, The received signal is induced into the coil 14 of the receiver circuit R rectified and somewhat amplified by said receiver circuit and induced in the form of voice modulated current into the secondary 16 of transformer 15 which transformer may or may not be provided with a core of magnetic material. The circuit from secondary coil 16 to the listening-in line 26 comprises conductors 18 and 34,

contacts 19 and 33 of the T & R relay 17 this relay being at the time de-energized, conductors 136 and 137, contacts 20 and 31 of relay 21, conductors 22 and 30. contacts 23 and 29 of relay 24, and conductors 25 and 28.. The listening-in line 26 terminates in jack 27 and the controlling oierators telephone is connected to that jac The operator upon hearing the call and determinin the location of the train, selects idle trun line 35, and plugs into jack 71 with plug 69 of cord circuit 70 (see Fig. 3). She then winds the impulse sender 38 and releases it. The contact 39 of the impulse sender, 38

is thereupon operated to send out a definite combination 0 positive impulses operating selector 36 at radio station A. The circuit from impulse sender 38 to selector 36 comprises contact 39. conductor 41, battery 40, conductor 57 to point 56, conductor to point 51, conductor 53, armature 52 of relay 49 and 36, conductor 50, armature 48 of relay 49 and its contact, conductor 47 to point 46, ring side of trunk line 35 to point 45, conductor 44 to;

point-43, conductor 42 to contact 39. Contact 58 is closed by the operation of selector 36, and relays 24, 59 and 60 are thereupon en ergized, their circuits being closed by contact 58.

Energizing relay 60 breaks contacts and 66 thus disconnecting selector 64, thereby preventing its operation. Energizing relay 24 breaks contacts 23 and 29, disconnecting the radio apparatus from the listening-in line a energizing relay 59, closes contacts 62 and 93 connecting the radio'applaratus to the trunk line. Contact-.62 is in t e circuit of step bystep magnet 109 of the wave length mechanism, and. since that contact is now closed the wave length mechanism can be operated by the controlling operator.

The circuit whereby the controlling opera tor operates the wave length mechanism comprises switch contact 108 at the Albany control; station, conductor 118 to point 117, conductor 116, electromagnet 109, conductor 115 to point 137, conductor 87, contact 62 of relay 59, conductor 77 to point 78, ring side of trunk line 35 to point 113, conductor 112, battery 111, and contacts 108.. Each time contact 108 is closed, electro-magnet 109 is energized and the wave length switches are advanced one step. A- suitable switching mechanism would ordinarily be provided for operating contact 108 the. required number of times for any desired wave length.

The circuit for operating the T 85 R relay is controlled by switch contact 82 and comenergized the circuit from primary coil 89 of transformer 90 to trunk line 35, comprises conductor 88. contact 74, conductor 87 contacts 62 of relay 59, conductor 77 to point 78 onthe ring side of the trunk line, point 85 on tip side of trunk line, conductor 94, contact 93 of relay 59,. conductor 92, contact 73 of T & R- relay 17 conductor 91 to primary coil 89 of transformer 90. just described for the T & R relay is associated with each of the trunks and the listening-in line.

Referring to the radio transmittin circuit T shown in Fig. 2, it will be noted t at condenser 95 is connected in circuit by virtue of switch member 99 being in the first or listening-in position. When switch member 99 is shifted to second, third, and fourth positions,

A circuit such as that condensers 96, 97 and 98 res ectively are connected into the circuit. y one of the lating circuit and consequently the wave 'length is varied. The wavelength of the receiving circuit .is likewise varied through the medlum of the condensers 104, 105, 106 and 107 and the wave length of the antenna is varied by means of condensers 9, 10, 11 and 12. The wave length of the transmitting circuit, receivingcircuit and antenna circuit is of course varied simultaneously.

The train being in track section 2, relay 138 is energized by battery 139 and the local circuit of signal lamp 140 is closed thus lighting that lamp. Signal lamp140 indicates to the operator the location of the train. When the train passes out of section 2, into section 3, and therefore out of the ran e of radio station A, and into the range 0 radio station B, signal lamp 141 will be lighted and lamp 140 will be extinguished. The operator is thus notified to transfer the connection from radio station A to radio station B, and this is accomplished by operating impulse sender 142, sending out a combination of negative impulses. Negative impulses will not afi'ect the selector of radio station A, as it is designed to operate only on positive impulses, and consequentl the radio apparatus at radio stationB will e connected to trunk line 35, while that at radio station A still remains connected thereto. However, after impulse sender 142 has finished sending its combination of negative impulses, the lug 143 will cause the operation of contact 144, thereby sending out one positive impulse which will operate to return selector 36 at radio station A to its normal position. Radio station A will thereupon be disconnected from trunk line 35 and connected to listening-in line 26. Relay 59 being de-energized by the opening of its circuit, its armatures will be restored to normal, breaking contacts 62, 93 and 122. But before contact 122 breaks, contact 123 will make thus momentarily establishing a circuit through release magnets 119 and 120 of the wave length mechanism, and battery 124. The holding pawl 126 and stepping pawl 125 will be thereby released, and the ratchet 127 together with switch members 13, 99, 100, 101 and 102 will be restored to normal, that is, the listening-in position.

The electro-magnet 149 of the impulse sender release mechanism Fig. 4 would ordinarily be connected in the circuits of signal lamps 140 and 141, and would'be energized upon a train entering the corresponding sections of the track. Referring to Fig. 3 it is seen that trunk line 35 interconnects two control stations and terminates in a 'ack at each end. Signal lamps and associated relays are shown for indicating busy lines. When-plug 69 is inserted in jack 71 a circuit will be established from battery 152 of cord circuit 70, at Albany through relay 151 at Utica energizin that relay; cau'sing its armature to be pulle up closing the circuit of signal lamp 150. Lighting of signal lamp 150 will indicate to the Utica operator that trunk line 35 is busy. When the train approaches Utica the Albany operator will call the Utica operator on the order wire or by other means not shown and ask the Utica operator to take over control of the connection. The Utica operator will insert plug 154 into jack 153 and the plug at the other end of the cord circuit 158, into the jack of a succeeding trunk line extending to Syracuse, the next control station. The operation is then a repetition of that which has been previously described. No flash back signal is shown for indicating to the Albany operator that the conversation has been completed and the connection may be taken down, but such signaling arrangements are old in the art and will be obvious. In the circuits described only one radio station is connected to the same trunk line at one time, but if desired the circuits can be readily modified so that more than one radio station can Es connected at one time to the same trunk In the event that an operator wishes to communicate with a train in her division, the position of which she does not know, she will plug her telephone set into the listening-in line jack and operate the T & R key associated therewith, thereby connectingthetransmitting apparatus at all the radio stations in her division or one of her divisions, as the case may be, to the listening-in line, and she may then speak through the medium of all the so-called radio stations simultaneously and ask for the position of the desired train. Upon receiving the necessary information from an operator on the wanted train, she will transfer the con-- nection to an idle trunk and proceed as previously described.

Two trunk lines 35 and 131 respectively are shown in Figs. 1 and 2. Two selectors 36 and 64 are shown at radio station A, co-operating with trunk lines 35 and 131 respectively and two relays 49 and 60 are shown co-operating with the selectors. \Vhen selector 36 is operated and contact 58 is'closcd, it will be seen that the circuit of relay 60 will be energized, and contacts and 66 will be open cutting off selector 64. Likewise if selector 64 were operated. relay 49 would be energized cut- "til functions of relays 24, 59 and 60 can be per formed by a single relay. Greater simplicity of illustration is accomplished, however, by showing three relays instead of one. Furthermore it is obvious that these relays can be entirely eliminated by the use of a selector designed to directly operate the contacts operated by these relays.

Where a system in accordance with this invcntion is utilized as a broadcasting system, the automatic selectors at the radio stations may, if desired, be eliminated, and the radio apparatus can be connected directly to a transmission line or through the medium of plugs and jacks or the like. But it is preferable to retain the selectors, as it may be desirable at times to broadcast through only one or two stations at a time. Where the specific arrangement shown and described herein is used for broadcasting purposes, either the listening-in line or a trunk may be employed as the medium for transmitting the signals from the control stations to the radio stations. The signals to be broadcasted may be transmitted from any of the control stations and ifito'the ether through the medium of all the radio stations simultaneously.

What is claimed is:

1. In a radio signaling system comprising a plurality of stations arranged for intercommunication on a plurality of carrier frequencies, means for establishing communication with a plurality of stations on any given carrier frequency and a selective callmg mea'ns for selecting any one of said plurality of stations.

2. In a signaling system including a plurality of radio stations arranged in multiple along a trunk line, a control station connected with said line, tuning means at each radio station whereby all of said radio stations may operate on the same normal wavelength, and means operable from said control station to change the wavelength at each radio station from the normal wavelength to another wavelength individually difierent for each radio station.

3. In a signaling system including a plurality of radio stations arranged in multiple along a trunk line, a control station connected with said line, selective means operable from said control station whereby said radio stations can be individually put into and out of communicative relation with said trunk line, and wave-changing means operable from said control station conjointly with said selective means whereby all of said radio stations are tuned to operate on the same wavelength when out of communicative relation with said trunk line, and on an individually different wavelength when in communicative relation with said trunk line.

In testimony whereof I aifix my signature.

CROSBY R. GAUTHIER. 

